This invention concerns the conveying of particulate materials and more precisely conveying materials that agglutinate. Foundry molding sand contains binders and agents that enable it to retain a desired shape after it has been removed from a mold. Transporting such sand on a conveyor can cause the sand to stick to the conveyor surface and to pack into large accumulations that block the conveyor, and such packing is especially severe on vibrating conveyors. Prior attempts to prevent or to break up such accumulations of packed sand by lining a conveyor with a flexible sheet material and flowing air under such sheet material have not been entirely successful. They have required the use of an excessive volume of air, which results in high capital and operating costs. Also, any holes or leaks in the sheet material renders the system ineffective for clearing packed material off the conveyor. And when the sheet material liner is sealed to the bottom of the conveyor at its sides, material packed against the upper sides or in the corners of the conveyor is not always dislodged.